In certain machines it is desirable to be able to measure the load on internal components of the machine. For example, in a wind turbine it is desirable to be able to measure the load on certain bearings.
Many different load measurement devices are available, but often at least a certain amount of disassembly of the wind turbine is required in order to gain access to the bearing.
One possibility for mounting a sensor to measure a load on a bearing is to drill a hole through a part of the component in which the bearing is housed and mount a sensor in that hole. Alternatively, a hole that is present in the component may provide a suitable location to mount a sensor, for example a hole that receives a bolt which is used to remove the bearing from the component may be used.
Strain gauge sensors which can be mounted in holes are well known.
One such strain gauge is described in U.S. Pat. No. 2,873,341. This strain gauge comprises a bolt having a central bore in which is mounted an epoxy core with a resistance wire is embedded therein.
The bolt strain gauge described in U.S. Pat. No. 2,873,341 has the strain measuring element in the centre of the bolt, which is not ideal for measuring strain in a component situated at the end of the bolt.
A more suitable form of strain sensor is a friction strain sensor. Such strain sensors are used in many applications. Such friction strain gauges must be pre-loaded to a certain extent in order to function. Furthermore, friction strain gauges are very sensitive to damage, for example when subject to shear forces. Friction strain gauges are described in general terms in GB 2,367,628.
There seems to be room for improvement.